The field of the present invention relates to electric motors, particularly to small electric motors used in equipment such as synchronous sound motion picture cameras, in which it is desireable to minimize the noise and vibration produced by the motor. In the motion picture industry, the electric motor which drives the film advance mechanism is desirably small but requires a relatively high power output. In addition and particularly in a synchronous sound camera, it is highly desirable to minimize noise and vibration produced by the camera to avoid recording the noise on the sound track or transfer vibration to the filming mechanisms.
There have been many attempts to dampen noise and vibration in electric motors. In U.S. Pat. No. 3,546,504, layers of elastic material having high inherent dampen properties are positioned (a) between the motor shaft and the bearings, (b) between the bearings and the bearing flange and (c) within the rotor shaft itself. An additional layer of elastic damping material is also placed between the circumference of the stator lamination packet and the supporting arm.
Similarly, Great Britain Patent No. 1,207,145 discloses an electric motor having a layer of resilient material interposed between the bearing seat and the outer ring of the ball bearing. In the devices of both U.S. Pat. No. 3,546,504 and GB 1,207,145, a layer or sheet of resilient material is positioned between certain parts. However these layers of resilient material must be specially manufactured or cut to size and the motors themselves must be substantially modified in order to accommodate these layers. In addition the amount of damping is highly dependent upon the damping properties of the resilient material itself as well as the thickness chosen for the material
In addition, the installation of the layers of resilient material would not be readily implemented upon an existing motor but would likely require design considerations at the manufacturing stage. The present inventor has recognized it would be desireable for an electric motor to be readily modifiable either by the manufacturer or the skilled purchaser.